1. Field of the Invention
The present invention relates to a process for the erasure of information recorded in an optical information medium. More specifically, the present process pertains to an erasure procedure which invokes the adjustment of certain defined parameters in order to effect accurate, efficient and clean erasure of the information desired to be erased.
2. Description of the Prior Art
The accurate and efficient erasure of information patterns in an optical information medium has long been a problem. Various techniques of irradiating and/or heating an optical information medium in order to effect erasure have been attempted.
Techniques for erasing film deformation patterns are particularly widespread. Generally, such techniques have involved heating the film, generally a thermoplastic, sufficiently above its melting point so as to cause surface tension to smooth out the thermoplastic surface. The heating can be global or localized, e.g., by use of a laser beam. When a laser beam is used for the erasure procedure, various alterations in a parameter such as the laser power or focus offset have been made in order to effect the erasure.
U.S. Pat. No. 4,264,986 discloses a method for recording and erasing information in an optical information medium. In the process, a pulsed laser beam is used to inject a pulse of heat energy into a smooth-surfaced recording medium to produce a recording mark left on the surface of the recording medium in the form of a crisply-defined pit or crater. Erasure is achieved by adjusting the intensity of the pulse of laser radiation injected into the recording medium. In the case of a pit or crater, for instance, the depressed area is thereby remelted and raised to a temperature such that a rate of cooling is achieved which results in the remelted volume solidifying to its original state of specific volume, so that the pit is erased and the surface of the medium is restored to its original smooth condition.
In the article "Reversible Read-Write-Erase Properties of Styrene Oligomer Optical Recording Media," Japanese Journal of Applied Physics, Vol. 22, No. 2, Feb. 1983, pp. 340-343, there is discussed a total surface heat erasure procedure and a scanning erasure procedure for the erasure of a sequence of pits. In the scanning erasure procedure, the writing objective lens is moved exactly 10 microns out of focus towards the medium, and then the disk surface is irradiated with 10 mW of laser light from a He--Ne laser by moving the light beam in the direction of the pit sequence at a speed of 1 mm/sec.
Another procedure for the erasure of a deformation pattern is described in U.S. Pat. No. 3,475,760, issued to Carlson. The patent discloses a system for recording information as a deformation pattern on a thermoplastic medium by scanning the medium with a high energy small diameter laser beam capable of directly forming a schlieren-readable deformation pattern in the medium without having to provide an electrical charge pattern. Selective erasing of a previously recorded deformation pattern on the medium is provided for by simply recording over the area to be erased using a similar laser beam as used for the previous recording but with a smaller scan line spacing.
U.S. Pat. No. 4,599,718 discloses a method for erasing a light recording medium comprising a thermoplastic resin having a number average molecular weight of 30,000 or less wherein an information pit is refilled by using a light beam diameter greater than the pit diameter.
Suitable apparatus for erasure of information on an optical recording medium is disclosed in U.S. Pat. No. 4,712,207.
Erasure of information patterns other than deformation patterns has also been suggested. For example, note U.S. Pat. No. 4,425,570, issued to Bell et al., which pertains to a reversible recording medium and information record wherein the light absorptive layer is a granular material comprising domains of a light sensitive material embedded in a dielectric matrix. The domains comprise a material which can be reversibly switched from a first state to a second state having different optical properties by the absorption of light. Useful materials include tellurium, selenium or alloys containing these materials, arsenic triselenide, arsenic trisulfide and other chalcogenide alloys where absorbed light produces a change in the degree of crystallinity.
U.S. Pat. No. 4,710,911 discloses a method of erasing optical information from a state-changeable photosensitive recording film which comprises initially irradiating an area on the recording film at a power level sufficient to raise the temperature of the film above its melting point. Erasure is then effected by a slow cooling of the film through a slow reduction in the power of the light irradiating the film.
The problem to date, however, is that the erasure techniques heretofore known have often resulted in noisy, i.e., not clean, or incomplete erasure. As well, erasure is often times accompanied by or the result of gouging or additional writing. This results in a noisy record of information. It would be preferable to return the medium to a clean, unwritten state upon erasure. A process for avoiding these disadvantages, therefore, is most desired in the art. Indeed, a process which can provide accurate, fine-tuned yet complete erasure would greatly enhance the commercial viability of optical information media.
Accordingly, it is an object of the present invention to provide a novel process for the erasure of an informaton pattern recorded in an optical information medium which overcomes the aforementioned problems.
It is another object of the present invention to provide a process for erasing information in an optical information medium wherein, specifically, the information is in the form of pits.
Another object of the present invention is to provide a process for the erasure of information recorded in an optical information medium which effects accurate yet complete erasure of the information.
Still another object of the present invention is to provide a process for the erasure of information recorded in an optical information medium which effects erasure without additional writing on the medium or gouging of the medium.
Yet another object of the present invention is to provide an efficient process for the erasure of information recorded in an optical information medium which effects erasure and leaves a noise-free background.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the foregoing description, the drawing and the appended claims.